Soft x-ray device with demountable electrodes



Jan. 27, 1970 J. LEWIS, JR 3,492,521

SOFT X-RAY DEVICE WITH DEMOUNTABLE ELECTRODES Filed Oct. 31, 1967 2 Sheets-Sheet l INVENTOR JOHN LEW/5, JR.

BYAM"; Me

MWATTORNEY Jan. 27, 1970 3,492,521

SOFT X-RAY DEVICE WITH DEMOUNTABLE ELECTRODES Filed Oct. 31, 1967 J. LEWIS, JR

2 Sheets-Sheet 2 INVENTOR JOHN LEWIS, JR.

Y E N R O n A United States Patent 3,492,521 SOFT X-RAY DEVICE WITH DEMOUNTABLE ELECTRODES John Lewis, Jr., 2838 Cherry St., Falls Church, Va. 22042 Filed Oct. 31, 1967, Ser. No. 679,401 Int. Cl. H01j 35/04 US. Cl. 31355 8 Claims ABSTRACT OF THE DISCLOSURE The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention is directed to ultra-soft X-ray source tubes and more particularly to the insulator and electrode assembly for proper operation of the X-ray source while permitting quick assembly and disassembly of the tube.

This invention is an improvement over an ultra-soft X-ray source tube such as disclosed in Patent No. 3,138,729 (FIG. 4). In operation of such tubes, it is well known that the target axis must lie in the vertical plane and that the alignment is critical, for instance, one tenth (0.1) degree. Also, the assembly must be vacuum tight. An existing problem is brought about by the process with which the electrodes are brought through the base support and which are connected thereto. Heretofore, a ceramic feed-through was brazed to the base support. This required special jigs for alignment and high temperatures for brazing. Such a feed-through was usually off in alignment and also was subject to vacuum leaks after short periods of use. Satisfactory use of the X-ray generator tube requires that the target be properly aligned, that it has long life.

The present invention is directed to an improvement which results in a properly aligned target which is vacuum tight and one which has long life.

It is therefore an object of the present invention to provide a vacuum tight feed-through which is properly aligned and has long life.

Another object is to provide an X-ray target feedthrough which does not require :brazing of any of the parts.

Still another object is to provide a target feed-through which positions any heat affected seals in a safe unaffected area.

Yet another object is to provide a target feed-through which is easily disassembled and assembled in order to change targets and to provide a good vacuum seal While maintaining proper alignment.

While another object is to provide an X-ray assembly which is adaptable for changing targets, which has durability for long life.

The nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawing, in which:

FIG. 1 illustrates an exploded view of the several parts of the insulators and electrode assembly.

3,492,521 Patented Jan. 27, 1970 FIG. 2 is a cross sectional view illustrating the relationship of the parts in an X-ray assembly.

Now referring to the drawing, there is shown by illustration in FIGS. 1 and 2 the various elements of the invention wherein like reference characters refer to like elements throughout the drawing. As shown, the elements are assembled together and secured to a metallic base plate 10. The base plate has a flat upper surface 11 and a bottom 12 from which spaced cylindrical elements 13 and 14- extend. These spaced cylindrical elements are milled to provide axially aligned passages 15 and 16 therement with the base. The elements 13 and 14 extend from the bottom of the base plate to provide proper alignment of insulator-electrode assemblies that pass through the elements 13 and 14 and which are secured to the base plate. The upper surface of the base plate is provided with recesses 17 and 18 that provide shoulders 21 and 22 respectively about each of the passages 15 and 16 to receive a flange on the outer surface of the insulator elements. The base plate is also provided with suitable threaded holes 23 for securing a holddown plate 24. thereto by screws 19 which secures the insulator-electrode assemblies to the plate in axial alignment. That is, the axes are parallel to the base plate axis and to each other for proper operation of the X-ray tube. The base plate is also provided with suitable slot means 20 for securing the base plate to an appropriate envelope which is well known in the art and not shown for simplification of the drawing. The slots permit rotation of the base plate for twenty degree rotation which permits adjustment of the X-ray generating surface relative to the slot through which the X-rays pass through the exit slot. Such a housing or envelope is shown in Patent No. 3,138,729.

The electrodes of the X-ray tube of the present invention are operationally the same as that shown in the above patent; however, the shank portion and mechanical connections have been modified to conform to the insulator element to insure proper alignment and a vacuum seal that is durable and has long life. Such an arrangement enables one to disassemble and assemble the electrodes many times for changing the target elements.

The assembly includes elongated tubular insulator elements 25 and 26, each of which are provided with a flange 27 about the outer surface thereof. The outer diameter of each insulator element is such that the lower portion will have a close fit with the wall of the passage through which it fits and the flange and has a diameter such that it will fit into the recess about the passage with a close fit. As shown, insulator element 25 has smaller inner and outer diameters than that of insulator 26 and receives therein a smaller diameter electrode. The wall thickness and length of the insulator depending on the material of the insulator, the voltage and current which passes through the insulated electrode. The portion of each insulator that extends above the flange thereon has a greater outer diameter than that portion which extends below the flange. As shown, the upper end of insulator 25 includes a shallow recess 28 that forms a shoulder 29 and insulator 26 is milled on the inner surface to form a shoulder 31. An insulator bushing 32 having the same inner diameter as the insulator 26 and a thickness the same as the milled out portion is provided with a flange 33 on the upper end that extends over the upper end with the same outer diameter as that of the upper end of the insulator 26. The length of the bushing is sufficient to apply force onto an indium seal 34 placed onto shoulder 31.

Anode 41 is provided with a flange 42 that extends outward with the same outer diameter as the lower end of insulator 26 and the upper end of the electrode is provided with threads 43 to receive a nut 44 thereon. The outer edges of the nut is on a circle which has the same diameter as the outer diameter of insulator 26 and the flange on bushing 32. The target end 45 of the anode is the same as that described for Patent No. 3,138,729, FIG. 4.

Cathode element 46 is provided with a stepped flange 47 on the upper end which has a portion that fits into the recess in the upper end of the insulator 25 and a portion that extends out over the upper end of the insulator. The portion that fits into the recess secures an indium seal 34 between the shoulder of the insulator and the bottom surface of the flange on the cathod element. The cathode extends down through the insulator with a close fit and has a tapered split end 48 of smaller diameter than the portion that extends down through the insulator. A nut 49 having a tapered end screw threads onto tapered end 48. The cathode includes a threaded portion 51 just above the tapered threaded end 48 over which a sleeve 52 fits. The sleeve 52 has threads 53 on the inner surface of the lower end which threads onto the threaded portion 51 by use of spaner Wrench holes 50. An insulator spacer 54 is placed over the cathode above the sleeve 52 and is used when securing the cathode within the insulator sleeve 25.

A cathode filament 55 of electron emission wire such as shown in Patent No. 3,138,729 is secured between the cathode electrode 46 and the end of a barrier or shielding electrode 56 which is connected at the opposite end to the metallic base plate. The filament 55 is connected to the cathode electrode 46 by inserting the end into the slit 57 and then the nut 49 is tightened to close the slit against the filament wire. The opposite end of the filament is connected to the end of the barrier electrode by threading the end through an aperture and by use of a screw 58 that screw threads into a threaded hole against the wire end of the filament which seats against set screw 59. As noted, a focusing electrode 61 extends along the filament in parallel relationship and is secured to the end of the barrier electrode by use of screw 58 that passes through an aperture in the end of the shielding electrode. The cathode operates as disclosed in Patent No. 3,138,729 to generate electrons which are controlled and directed onto the target material for generating X-rays.

On assembly the barrier or shielding electrode is properly positioned and secured in place to the bottom surface of the base plate. Indium sealant material is placed in the recesses in the base plate around the passages therein then the insulator elements 25 and 26 are inserted into their proper aperture through the base plate with their flanges in the recesses and secured in place by placing the hold down plate 24 over the ends. The hold down plate is then secured in positioned by suitable screws. The target surface material is secured to the X-ray generating end of the anode then the anode electrode is inserted into the insulator 26 from the bottom up until the flange 42 rests upon the bottom of the insulator 26. The indium sealant is positioned in place on the shoulder provided in the upper end of the insulator. The bushing 32 is then slid over the upper end of the anode electrode and into the cutout area of the insulator such that the bottom surface rests on the indium seal while the flange 33 rests on the upper end of the insulator. Nut 44 is then screw threaded onto the upper threaded end and tightened down against the bushing. The bushing is forced against the indium seal while pulling the anode electrode flange tight against the bottom of the insulator. Such a construction makes the assembly vacuum tight and positions the indium seal sufliciently from the hot end of the anode such that the seal is not atTected by the heat.

The cathode electrode is then assembled by inserting the bottom end of the electrode into the top end of insulator 25. Indium sealant is placed around the electrode in the recess at the top of the insulator. The electrode is then moved downwardly until the flange 47 seats into the recess in the insulator. The spacer 54 is placed over the bottom of the electrode and the threaded sleeve 52 is screw threaded onto the threaded portion 51 of the electrode. The threaded sleeve is tightened, forcing the flange 47 against the indium sealant thereby sealing the electrode for vacuum tightness. It is noted that the indium seal is removed from the heated area and will not be affected by the heat. The ends of the cathode filament 55 are then threaded into the slit 57 in the bottom end of electrode 46 and the other end of the filament threaded into the lower end of barrier electrode 56. The nut 49 is tightened which squeezes the slit end tight against the filament end thereby holding the filament to the cathode electrode. The opposite end is secured in the end of the barrier electrode by use of a threaded screw. The focusing electrode is then secured to the end of the barrier electrode by use of a set screw.

The electrodes are all assembled and held in place so that their axes are parallel to each other and to the axis of the base plate. Thus, the elements are properly aligned, are vacuum tight, may be easily assembled and disassembled, and the seals are positioned such that they are not affected by heat from operation of the tube. Thus, the arrangement of insulator and electrode assembly of this invention brings about an X-ray tube which has long life. Also, the tubes may be easily disassembled to change the target surface without any deleterious effect on the elements of the tube. Further, the elements are assembled without brazing; therefore, the seals in the base plate are not affected by high heat required to braze the elements.

As noted in the drawing each of the electrodes is hollow over most of its length. This is for the purpose of admitting water to cool the electrodes during operation such as is well known in the art and shown by illustration in the above mentioned patent.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. In combination, a demountable self-aligning insulator-electrode vacuum tight feed-through assembly for a high voltage, high current, high temperature operation such as an X-ray tube which comprises:

a metallic base,

at least one passage through said base,

a recess about said passage,

a shoulder formed by said recess about said passage coaxial with said passage,

a tubular insulator,

a flange on the outer circumference of said insulator,

said flange having a diameter slightly less than said recess and a thickness of about the same depth as said recess,

said tubular insulator adapted to be positioned within said passage with said flange within said recess with a close fit, coaxially with said passage,

2. plate means having passages therethrough adapted to be placed over said flange on said insulator for securing said insulator to said base,

a cylindrical electrode,

said electrode having a diameter slightly less than the inner diameter of said tubular insulator and adapted to be positioned coaxially within said insulator with a close fit,

a flange on the outer circumference of said electrode,

said flange having a diameter substantially the same as the outside diameter of said insulator to prevent said electrode from passing entirely through said insulator,

said electrode including screw threads on the end from said flange,

a nut means adapted to screw onto said threaded end of said electrode to secure said electrode vacuum tight within said insulator.

2. In an insulator-electrode assembly as claimed in claim 1; which includes:

a recess in the end of said insulator within which said flange on said electrode fits with a tight fit. 3. In an insulator-electrode assembly as claimed in claim 2; which includes:

a seal within the recess of said base between said flange on said insulator and said base; and

a seal between said flange on said electrode and said recess in said insulator end.

4. In an insulator-electrode assembly as claimed in claim 1, in which said base plate includes a slot means for adjustably securing said base plate in place.

5. In combination, a demountable self-aligning insulator-electrode assembly; which includes,

a metallic base a pair of passages through said base with their axes in alignment,

a recess formed within said base around each of said passages,

a shoulder formed by said recess about each of said passages coaxial with each of said passages,

a pair of tubular insulators,

a flange on the outer circumferential surface of each of said insulators,

said flange having a diameter slightly less than said recess about said passage and a thickness of about the same depth as said recess,

each of said tubular insulators adapted to be positioned within one of said pass-ages with the flange thereon within said recess about said passage a close fit coaxially with said passage,

a plate means,

said plate means having passages therethrough and adapted to be secured to said base over said flange on said insulators to secure said insulators to said base,

first and second electrodes,

each of said electrodes adapted to be positioned in one or said insulators and having a dimension perpendicular to its linear axis which is less than the inner dimension of said tubular insulators perpendicular to the axis thereof thereby fitting coaxially in said insulator with a close fit, a flange on the outer circumferential surface of each of said electrodes, said flange having a dimension substantially the same as the outside dimension of said insulator within which the electrode fits to prevent said electrode from passing through said insulator, said first and second electrodes including screw threads thereon removed from said flange thereon, first and second nut means adapted to screw onto said first and second electrodes, respectively, to secure said electrodes in coaxial alignment within said insulators in a vacuum tight relationship. 6. In combination, in an insulator-electrode assembly as claimed in claim 5, in which,

said first electrode includes a screw threaded slit endnut means on the end thereof for securing a filament wire thereto, and said second electrode includes a metal target surface on one end thereof. 7. In combination in an insulator-electrode assembly as claimed in claim 6; in which,

said flange on said first electrode is removed from the end to which said filament is secured, and said flange on said second electrode is adjacent to said metal target and the screw threaded end is on the end opposite from said metal target end. 8. In combination in an insulator-electrode assembly as claimed in claim 5 wherein,

said insulators are formed by a boron nitride ceramic.

References Cited UNITED STATES PATENTS 12/1961 Goss 313- X 6/1964 Henke 3l357 US. Cl. X.R. 250; 3l357, 237 

